(1) Field of the Invention
The present invention relates to transmission devices, and more particularly, to a transmission device that performs a multiplexing transmission control in SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy).
(2) Description of the Related Art
As is known, SDH/SONET has been standardized as a signal hierarchy multiplexing system in digital transmission, and development of economical digital networks has been progressed. A further progress of multimedia networks has been expected.
FIG. 17 is a schematic block diagram of a conventional synchronous multiplexing transmission device. A synchronous multiplexing transmission device 100 is arranged in a SONET/SDH network, and is made up of a processing selection part 101, a demapping part 102, cross-connect parts 103, 104, a mapping part 105, and an output selector 106. The following description is directed to the transmission device 100 that is designed to work on SONET.
The processing selection part 101 receives an STS-n (Synchronous Transport Signal: n denotes n times of STS-1), and determines whether the received signal should be cross-connected as STS stands or should be converted into a VT (Virtual Tributary) before cross-connection. Then, the received is output to one of the two routes on the basis of the determination result.
The demapping part 102 converts the received STS signal into low bit rate VT signals by demapping (high-to-low bit rate changing). The cross-connect part 103 makes cross-connecting on the VT basis, and the cross-connect part 104 makes cross-connecting on the STS basis.
The mapping part 105 maps VT signals from the cross-connect part 103 to yield an STS signal (low-to-high bit rate changing). The output selector 106 selects either the STS signal that has been cross-connected on the VT basis or the STS signal that has been cross-connected on the STS basis.
The synchronous multiplexing transmission device 100 separately processes the STS signal and VT signal. This increases the circuit scale and power consumption and prevents downsizing.
Recently, the backbone networks have a huge capacity due to an increased demand along with wide spreading of Internet, and the transmission device has been strictly required to have an increased integration density, an increased transmission capacity and advanced functions. It is increasingly important to make an effort on further downsizing and reduction in power consumption in circuit design.